>i've done some work on the 3A circuit and it's
>looking do-able.

Thats fantastic, at 2-3A it becomes very very useful.

>But i'm getting worried about clogging the piclist
>with too many SMPS posts so if anyone asks this to be
>taken offlist we should.

No problem. If anyone objects or you'd like to do any more off-line
just let me know.  This really is too good a thing not to be kept in
front of anyone who could use it (IMHO).

>But I THINK i've got a good working 3A SMPS regulator
>solution for very low parts cost. :o)

Cheap is good ;-]

>I just built a big version of my 2-tran regulator
>using a cheap TO220 darlington, there are a heap of
>"old" parts to buy cheap these days, say 100v 5A
>types that all do under 1.0v saturated at 3A. Doesn't
>sound that impressive, but they are CHEAP and in
>one package.

Too true. I bought a handful over the summer and paid about
2 bits each for new ones.

>By comparison, the Maxim Max727ECK switcher chip you
>mentioned has 1.7 volts saturated at 2A! That's not real
>good if you want a 2A switcher. So the cheap darlington
>is about 1W to 2W more efficient, AND allows 3A or more
>continuous loads as an added bonus.

That really is an improvement. I thought the Max727 or the LM2576
were a real answer to things but your switcher seems like a real
improvement.


>Well the 2-tran solution is cheap! I'm using a 50 cent
>darlington and a small signal transistor. The inductor and
>buck diode costs you have with both circuits. It will be
>more efficient than the 2A chip, and will do 3A, but the
>ability to handle wide input voltages is not perfect
>with it.

At what point ie high end or low end will there be a problem with
the input voltage? Would it be better to build a high and a low input range
or any problems really just going to show as a loss in efficiency?

>Now you've said its for 24v auto use that gives a
>decent range (16v to 32v?) which should be tunable
>with the CHEAP circuit i'm using now. If you want the
>ability to go down to real low voltages as well it will
>cost an extra transistor as a constant current source
>for the zener monostable.

Well 80% of what I'm thinking of using this for would be
auto voltages ie 12-13.8vdc, then say 10% around 30vdc
and possibly the rest being run off of a battery pack which
might be 7.2-9v which is the absolute lower limit.

I''d even like to try and adapt this to re switching regulator
on a bike alternator. That put out 40.

>So the 5v 3A version of my regulator is now working
>for very low cost, and about 83% efficiency without
>needing a special FET etc, but before I write it up etc
>can you confirm input voltage ranges and any other
>details you might need. Do you really need that 7v
>to 35v input range at full power and max efficiency?

It solves any foreseeable use I would have. What about
  setup that is optimized for a high or low range? ie both
retain the 5Vdc 3A out but say the first would work 7.2v
to 15v and the second might be optimized for 20-35v.
Not to make any work but is it easier to define it over a
smaller range to maximize the conversion efficiency?

Cheers

Dave

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